1. Field of the Invention
The present invention relates to a charging member to be used in an electrophotographic apparatus, an electrophotographic apparatus, and a process cartridge.
2. Description of the Related Art
In an electrophotographic apparatus, a contact charging mode has been adopted as a process for subjecting a surface of an image bearing member such as a photosensitive member or a dielectric member to a charging treatment. As a charging member to be used in the contact charging mode, there has been used an elastic roller having an elastic layer containing a rubber or a thermoplastic elastomer in order to ensure a uniform nip width (close contact width) with an object to be charged and to prevent the object to be charged from being damaged. Such elastic roller is generally brought into pressure contact with an image bearing member by applying a predetermined force to an axis at both end portions of the elastic roller. Hence, there is a tendency that nip pressures at end portions are high as compared to a nip pressure at a central portion in a longitudinal direction of the elastic roller. Therefore, in the case where such elastic roller is applied as the charging member to the electrophotographic apparatus, dirt is liable to be accumulated at the central portion in the longitudinal direction of the elastic roller through formation of electrophotographic images over a long period of time. In addition, the dirt causes streak-like unevenness on the electrophotographic images in some cases.
Meanwhile, Japanese Patent Application Laid-Open No. 2006-119451 mentions the following problem. That is, when an elastic roller is abutted on an image bearing member, a nip width does not become uniform in a longitudinal direction of the elastic roller, and hence a distribution occurs in nip pressure, resulting in toner dirt and image unevenness. In addition, Japanese Patent Application Laid-Open No. 2006-119451 describes that such problem can be solved by modifying an outer peripheral surface of the elastic roller, that is, a surface of an elastic layer at different treatment levels in a thrust direction of the elastic roller. Japanese Patent Application Laid-Open No. 2006-119451 mentions ultraviolet irradiation and electron beam irradiation as specific examples of a method for the modification of the surface of the elastic layer.